1. Field of the Invention
The present invention relates to a composition for rust prevention of metals. More particularly, the present invention relates to a composition for rust prevention of metals which is stably present at room temperature, and when coated on metal surfaces, forms an effective film by the action of water present in the air or by slight heating, thereby exhibiting a good rust prevention property. Particularly, it relates to a composition for rust prevention suitable for copper, copper alloys, such as brass, nickel silver, etc. and metals coated with a chromate film having a color such as yellow, black, green or the like.
2. Description of the Prior Art
Treatement of metals for rust prevention has been conventionally conducted by various methods such as (a) a method wherein various coating compositions, for example, those of thermosetting resins, for example, epoxy resin, alkyd resin, polyester resin, acrylic resin, urethane resin and other resins, of solvent type, aqueous type or powder type, are applied to metal substrates and baked, (b) a method wherein thermoplastic resins such as polyolefins, polyamides, polyesters and the like are melt-coated on metal substrates, (c) a method wherein various oils (mineral oils, animal oils and vegetable oils) are coated on metal substrates, (d) a method of plating or surface-treating with a metal, a metal salt or the like. In methods (a) and (b) of applying a thermosetting or thermoplastic resin coating composition, a sufficient rust prevention cannot be exhibited even in a system where a corrosion-resistant pigment of chromate type, phosphate type or other types is added, unless the coating composition is applied in a thickness as large as 10 to 2,000 .mu.m. Further, because a high temperature is required for baking or melt-application of the coating composition, substrates may be impaired and heat energy may be lost. The method (c) of coating metal substrates with an oil is used only for temporary rust prevention and the oil which is originally a "stain" under the conditions under which the substrates are used is usually removed. The method (d) of surface-treatment gives much poorer rust prevention than the methods (a) and (b) of applying the above coating composition, and the surface treatment is ordinarily used to form an undercoat for the coating composition. Even in the case of metal-plating, for example, a chromate film is deteriorated when exposed to a high temperature of 50.degree. to 80.degree. C. or higher and loses its rust-preventing ability completely.